Preheat oven to 350° Fahrenheit. Lightly spray a 10” cast iron skillet with cooking spray and set aside. In a medium bowl, combine flour, cornstarch, baking soda, and salt. Mix briefly with a fork to combine and set aside. In a bowl of an electric mixer fitted with a paddle attachment (hand mixer and large bowl work here too), over medium/high speed, cream the butter and both sugars until light and fluffy, about 2-3 minutes. Add the eggs one at a time, beating well after each addition. Reduce the mixer speed to low and add the vanilla extract. Stop and scrape the mixer to incorporate ingredients. Turn the mixer speed to low and add the flour mixer all at once. Mix until mostly combined, about 20-25 seconds. It’s fine if you see some flour bits. Remove bowl from the mixer and fold in the chocolate chips. Spoon about ½ the cookie dough in the cast iron skillet. Spread evenly with an offset spatula. Spread the Nutella over the cookie evenly, starting at the center and working your way outward, leaving a small border. Spoon the remaining cookie dough and spread with an offset spatula and cover evenly. Place the skillet in the oven and baked for 25 minutes until the top has lost its shine, yet it remains under baked. Remove from the oven and allow to cool for about 10-15 minutes. Serve warm with scoops of ice cream.